1. Field of the Invention
The present invention relates to a cured form of calcium silicate and a reinforced calcium silicate composite structure, and also relates to methods for producing same. More particularly, the present invention is concerned with a cured form of calcium silicate, mainly comprising tobermorite and exhibiting a powder X-ray diffraction pattern in which the diffraction peak intensity Ib ascribed to the (220) plane of the tobermorite and the minimum diffraction intensity Ia observed in the diffraction angle range between the two diffraction peaks respectively ascribed to the (220) plane and (222) plane of the tobermorite satisfy the relationship Ib/Ia≧3.0; an apparent specific gravity of from 0.14 to 1.0; and a differential pore distribution curve obtained by mercury porosimetry in which the logarithmic width of the pore diameter distribution as measured at a height of ¼ of the height of the maximum peak of the differential pore distribution curve is from 0.40 to 1.20. The present invention is also concerned with a reinforced calcium silicate composite structure which comprises the cured form of calcium silicate and a reinforcing iron rod or a reinforcing wire netting. The present invention is further concerned with methods for producing the cured form of calcium silicate and the reinforced calcium silicate composite structure.
2. Prior Art
From the viewpoint of lowering the weight of a building, there has been a demand for incombustible and lightweight building materials in recent years.
As a building material meeting the demand, an autoclaved lightweight concrete (hereinafter, frequently referred to simply as an “ALC”) and a fiber reinforced calcium silicate board (hereinafter, frequently referred to simply as a “calcium silicate board”) have hitherto been used. An ALC is produced by a method which comprises: providing a cement material and a silica powder as main raw materials, and optionally, at least one material selected from the group consisting of a quick lime powder, gypsum and the like; mixing these materials together to obtain a mixture; adding water to the mixture to obtain a slurry; mixing the slurry with a foaming agent to thereby obtain a foamable slurry; and pouring the foamable slurry into a mold, followed by autoclaving. An ALC exhibits an apparent specific gravity of from approximately 0.5 to 0.6 and, hence, has a light weight. Further, an ALC contains a large amount of highly crystalline tobermorite (5CaO.6SiO2.5H2O) and, hence, has excellent long-term weatherability, excellent fire resistance and excellent durability. Therefore, an ALC has been widely used as a material for an external wall, a floor material and an internal wall of a building.
The modulus of elasticity of an ALC is in the range of from 1,700 to 2,500 N/mm2. Also, the compressive strength of an ALC is in the range of from 4 to 5 N/mm2. On the other hand, with respect to the flexural strength (which is an important property of a substance used as a plate-formed material), an ALC itself has a flexural strength as low as about 1 N/mm2. Therefore, an ALC has been used in the form of a composite structure having a reinforcing iron rod arranged therein, as a material for parts of a building, such as a wall, a floor and a roof bed. However, the ratio in an ALC of the modulus of elasticity to the specific gravity (hereinafter, this ratio is frequently referred to simply as the “relative modulus of elasticity”) is not satisfactorily high, so that, even when an ALC is used in the form of the above-mentioned composite structure as a panel, the ALC is likely to suffer a large deflection. Therefore, an ALC has a problem in that an ALC cannot be used in a part of a building which is carried by supporting members arranged at long intervals. Further, an ALC is defective in that, when used as a floor panel for a dwelling, an ALC exhibits poor insulation against noises generated due to the weight impact because the relative modulus of elasticity of an ALC is not satisfactory. Therefore, in such a case, it has been necessary to conduct a complicated operation, such as application of mortar onto the ALC panel for alleviating the defect of the ALC.
On the other hand, when a concrete material is used in the form of a reinforced structure having a reinforcing iron rod arranged therein, the design strength of the reinforced structure is determined taking into consideration the compressive strength of the concrete material. An ALC has a problem in that it has low compressive strength, so that the use of an ALC is inevitably limited. Especially, an ALC cannot be used in a high-rise building. Also, a conventional ALC is very low with respect to nail holding strength as compared to the nail holding strengths of timber and the like, thereby limiting the use of an ALC in a building, especially at the sites thereof, such as nail receiving sites of a base material for a roof or a roof board. The nail holding strength varies depending on the relationship between the modulus of elasticity and the compressive strength, such as the ratio of the compressive strength to the modulus of elasticity. In the case of an ALC, this ratio is low, so that when a nail is driven into an ALC, the ALC cannot stand a local distortion caused by the nailing, thereby causing a micro breakage around the nail driven into the ALC. Therefore, an ALC does not exhibit a satisfactory nail holding strength.
For improving the properties of an ALC, various methods have been attempted. Examples of such methods include a method in which the cell size distribution of an ALC is controlled, a method in which the ratio of closed cells in an ALC is increased, and a method in which the crystallinity of the tobermorite contained in an ALC is enhanced.
There has been a presumption that cells present in the surface and inside of an ALC act as cracks, so that the strength of the ALC is markedly lowered. Based on this presumption, research has been made. For example, Unexamined Japanese Patent Application Laid-Open Specification No. Hei 8-67577 discloses a method in which the number of cells in an ALC is decreased to thereby obtain an ALC having high specific gravity. However, this method has a problem in that, when it is intended to maintain the high compressive strength of an ALC in the method, it is necessary for the ALC to have an apparent specific gravity of at least about 1.1. That is, when the apparent specific gravity of the ALC is 1.0 or less, the compressive strength of the ALC is markedly lowered. In addition, the above-mentioned ALC produced by the method of the above-mentioned patent document exhibits a powder X-ray diffraction pattern in which, with respect to the diffraction peak intensity Ib ascribed to the (220) plane of the tobermorite and the minimum diffraction intensity Ia observed in the diffraction angle range between the two diffraction peaks respectively ascribed to the (220) plane and (222) plane of the tobermorite, the value of Ib/Ia is less than 3.0. This means that the tobermorite contained in the above-mentioned ALC has a low crystallinity as compared to a tobermorite which is generally contained in a conventional ALC and, hence, the ALC produced by the method of the above-mentioned patent document has unsatisfactory weatherability. Especially, this type of ALC is susceptible to a carbonation reaction (i.e., a neutralization reaction) in which the ALC is reacted with carbon dioxide contained in the air and is decomposed into calcium carbonate and noncrystalline silicate. That is, this type of ALC has unsatisfactory resistance to the neutralization reaction. Therefore, the above-mentioned ALC has a problem in that the use of the ALC as an external building material is inevitably limited.
Further, Unexamined Japanese Patent Application Laid-Open Specification No. Hei 7-101787 discloses a method for producing a cured, lightweight concrete material without using a foaming agent, wherein the cured material exhibits an apparent specific gravity of 0.7 or more and a compressive strength of more than 20 N/mm2. However, when the apparent specific gravity of the cured material is 1.0 or less in this patent document, the cured material is composed mainly of a hydrate of calcium silicate having very low crystallinity and, hence, has unsatisfactory weatherability, especially very poor resistance to the above-mentioned neutralization reaction with carbon dioxide in the air. Therefore, the cured material has a problem in that the use of the cured material as an external building material is inevitably limited.
In recent years, with respect to structural materials (such as an external building material and a floor material) in which reinforcing iron rods are arranged, there has been a demand for extension of the length of the structural materials and extension of the interval at which the structural materials are carried by supporting members. From this viewpoint, the structural materials are required to have three times the strength of a conventional ALC. For example, WO99-42418 discloses a method for producing a lightweight concrete material without using a foaming agent. Examples of such lightweight concrete materials include a material exhibiting an apparent specific gravity of 0.52 and a compressive strength of 10 N/mm2, and a material exhibiting an apparent specific gravity of 0.69 and a compressive strength of more than 19 N/mm2. However, the lightweight concrete material disclosed in this patent document exhibits a differential pore distribution curve obtained by mercury porosimetry in which the logarithmic width of the pore diameter distribution as measured at a height of ¼ of the height of the maximum peak of the differential pore distribution curve (hereinafter, this logarithmic width is frequently referred to simply as “logarithmic width at ¼ height”) is more than 1.20. When this type of lightweight concrete material is compared with a conventional ALC which has the same apparent specific gravity as that of the lightweight concrete material, the compressive strength of this type of lightweight concrete material is at most two times that of the conventional ALC. Further, there is a problem in that in this type of lightweight concrete material, the ratio of the compressive strength to the modulus of elasticity is unsatisfactory. Furthermore, there is still another problem in that this type of lightweight concrete material is produced without using a foaming agent and, hence, for producing this type of lightweight concrete material, a conventional apparatus employed for producing a conventional ALC cannot be used, so that the productivity of the lightweight concrete material is inevitably lowered. Moreover, it is impossible to obtain a lightweight concrete material having properties which are sufficiently improved to compensate for the lowering of the productivity.
On the other hand, a fiber reinforced calcium silicate board (calcium silicate board) is produced by a method comprising reacting a crystalline siliceous material and/or a non-crystalline siliceous material with a calcareous material, and curing the resultant reaction mixture together with a reinforcing fiber by autoclaving. A calcium silicate board is composed mainly of fiber, tobermorite, xonotlite, and a calcium silicate hydrate having a very low crystallinity (hereinafter, the calcium silicate hydrate is frequently referred to simply as “CSH”). The use of a calcium silicate board is roughly classified into a heat insulating material which exhibits an apparent specific gravity of 0.3 or less, a fireproof coating material which exhibits an apparent specific gravity of from 0.3 to 0.4, and a fireproof building material which exhibits an apparent specific gravity of from 0.6 to 1.2. A calcium silicate board having an apparent specific gravity of 0.4 or less is produced by a filter press method. On the other hand, a calcium silicate board having an apparent specific gravity of 0.6 or more is produced by a paper sheet making method.
A calcium silicate board contains fibers in an amount as large as 5 to 20% by weight, based on the weight of the calcium silicate board, so that the calcium silicate board has excellent flexural strength, excellent toughness and high processability. On the other hand, however, the calcium silicate board exhibits a high water absorption and a high shrinkage upon drying, so that the calcium silicate board exhibits poor dimensional precision. Further, the calcium silicate board is disadvantageous not only in that a large amount of dust is produced from a calcium silicate board, but also in that the calcium silicate board has a low surface hardness and, hence, is susceptible to flawing. Moreover, the calcium silicate board mainly comprising a CSH has poor weatherability and durability. Therefore, the use of this type calcium silicate board as an external building material is inevitably limited, and this type calcium silicate board is used mainly as an internal building material. Further, this type calcium silicate board is disadvantageous in that the calcium silicate board has a low compressive strength as compared to the flexural strength thereof, and has a very low modulus of elasticity, so that it is impossible to use, as a structural material, this type of calcium silicate board in the form of a structure having a reinforcing iron rod arranged therein.
For example, Unexamined Japanese Patent Application Laid-Open Specification No. Hei 3-237051 (corresponding to U.S. Pat. No. 5,330,573) discloses a shaped article of calcium silicate and a method for producing same, wherein the shaped article of calcium silicate comprises tobermorite, a CSH, quartz and a reinforcing fiber, and exhibits an apparent specific gravity of 0.55 and a flexural strength of 10 N/mm2 or more. In the method of this patent document, a siliceous material and a calcareous material are mixed with water at a temperature of 50° C. or lower for the purpose of elevating the tobermorite content in the shaped article of calcium silicate. However, the shaped article of calcium silicate exhibits a powder X-ray diffraction pattern in which, with respect to the diffraction peak intensity Ib ascribed to the (220) plane of the tobermorite and the minimum diffraction intensity Ia observed in the diffraction angle range between the two diffraction peaks respectively ascribed to the (220) plane and (222) plane of the tobermorite, the value of Ib/Ia is less than 3.0. That is, the crystallinity of the tobermorite contained in the shaped article of calcium silicate is very low as compared to that of a tobermorite which is generally contained in a conventional ALC, so that the shaped article of calcium silicate has an unsatisfactory weatherability, especially an unsatisfactory resistance to the above-mentioned neutralization reaction with carbon dioxide in the air. Accordingly, the shaped article of calcium silicate of this patent document cannot be used as an external building material. Further, due to the low crystallinity of the tobermorite contained in the shaped article of calcium silicate, the modulus of elasticity of the shaped article of calcium silicate is very low, so that it is also impossible to use the shaped article of calcium silicate of this patent document as a structural material.